Trucks for transporting pre-mixed concrete have a rotatable bowl which typically includes several internal helical fins. As the bowl rotates in one direction, the fins mix the concrete. When the bowl rotates in the other direction the fins move the concrete towards a discharge point of the bowl.
During normal operation of a concrete truck, residual concrete accumulates and hardens within the bowl, particularly in the vicinity of the fins. This residual hardened concrete reduces the capacity of the bowl, adds weight to the truck and can reduce the efficiency of the fins to mix and move the concrete.
Previous methods of removing hardened residual concrete include a worker entering the bowl and using a jackhammer to chip and break the concrete from the internal surface of the bowl and fins. This is a time consuming task which is very hazardous to the worker when in such a confined space. Additionally, there is a high potential for the internal surface and fins of the bowl to be damaged.
In order to address safety concerns, devices utilizing ultra high water pressure (up to 40,000 psi) have been used to remove hardened concrete. However, operation of these devices requires a trained operator due to safety issues surrounding the use of ultra high water pressure. Additionally, significant infrastructure is required to provide water at an ultra high pressure, which can result in high installation and running costs.
Daily washing of the bowl to remove concrete before it is cured can reduce the build up of concrete within the bowl. Previous methods of daily washing include loading a large amount of water into the bowl, rotating the bowl and then discharging the water. This method uses a large volume of water, and often does not remove concrete which has begun to cure. In particular, concrete located adjacent the fins is difficult to remove by this method.
The use of chemical agents in wash water has been postulated to assist in the removal of concrete residue. However, the use of these agents can contaminate later batches of concrete and also prevents the recycling of the wash water back into a concrete plant.